Crop Growth and Sex Expression

  

Cucumber is an annual deep-rooted (ca. 3 ft) crop with tendrils and hairy

leaves. The plants may have an indeterminate, determinate, or a compact plant

habit. The compact growth habit consists of plants with shorter internode

length than plants with indeterminate or determinate growth habit. Optimum 

growth occurs between 70-75F (20-25C), with growth reduction occurring

below 60F (16C) and above 90F (30C).

Several flowering habits exist in cucumbers. Most cultivars are monoecious,

with separate male and female flowers in the same plant. Gynoecious or "all

female" cultivars produce only female flowers resulting in up to 13 times more

female flowers than those obtained in monoecious cultivars. The so-called "PF"

hybrids produce predominantly female flowers but also produce a small

number of male flowers. Often "pollination" plants are supplied to insure 

fertilization on "PF" types. Many cultivars grown in greenhouses such as 

European cucumbers are parthenocarpic. Parthenocarpic varieties require no 

pollination for fruit production. In fact, pollination of these cultivars causes

 an off-shaped appearance of the fruit.

 The first flowers of monoecious plants are staminate or 'male' followed by 

pistillate or 'female' flowers from which fruits are born. Sex expression in 

cucumber may be affected by several factors such as plant density, plant

stress, temperature, and light intensity. Reduced rates of female flowers in 

gynoecious cultivars may result from exposure to stress caused by high plant 

population densities, insect attack, wind damage, and combinations of low light

intensity and high ambient temperatures. The commercially available hormone

etephon, at 125-250 ppm, increases the production of pistillate or female

flowers in gynoecious cultivars. Cucumbers will interbreed with other

cucumber cultivars but not with melons nor squash. Some markets, such as the

Japanese market, prefer 'bloomless' fruits, or fruit free of the natural film or

powdery tissue that cover the skin of cucumbers and several other vegetables.